The invention falls into the context of a high bit rate satellite communication system comprising at least one gateway linked to a server, or cluster of servers, making multimedia contents available via a server, a private network or the public internet network, a satellite link, and a set of terminals accessing the data of the server through the satellite link and the gateway.
The broadcasting of data via the satellite link according to a point-to-multipoint mode (to several identified recipients, or all the terminals present in a same satellite spot) rather than a point-to-point mode makes it possible to avoid performing multiple transmissions of a same content in parallel. This type of broadcasting nevertheless presupposes an a priori knowledge of the request linked to the multimedia content being routed. The choice of the routing mode for a multimedia content according to a point-to-point or point-to-multipoint broadcasting mode can therefore be made according to whether the content, like a TV or radio programme, is assumed to have an audience. This is called assumed popularity.
Some satellite solutions, such as, for example, the one described in the European Patent Application EP 2 480 004, propose adding memory spaces on the terminal side making it possible to store multimedia contents in order to make them available without delay to the users who request them after the broadcast. The most popular streams are then transmitted to be stored during time bands when the network load is less great.
However, these mechanisms are not applicable in the case where a multimedia content is unexpectedly requested by a number of users. They are subject to a decision as to the popularity of a content, which does not change as a function of the requests.
Another method, described in the patent U.S. Pat. No. 8,432,808 B1, consists in delaying the transmission of the content based on various criteria, then in broadcasting content according to a point-to-multipoint broadcasting mode. The criteria can be linked for example to the weight of the file, or to its popularity. By delaying the most popular contents as long as possible, the number of terminals having requested the multimedia content before its transmission increases. This mechanism makes it possible to optimize the satellite resource but presents the drawback of delaying the transmission of the multimedia content, thus increasing the latency of the communication system, and reducing the service quality. It also presents the drawback of applying only to the contents whose transmission can be deferred, and does not therefore apply to the multimedia programmes broadcast live.
The invention provides a solution that makes it possible to maximize the volume of multimedia content broadcast to each of the terminals via the satellite communication link by minimizing the number of retransmissions of a same content while reducing the resource requirements of the system.
Generally, the invention starts from the principle that the more popular a content becomes, the more it needs to be stored as close as possible to the users.
The invention does not introduce any additional latencies in the transmission, thus applying to the live broadcasts (streaming), but also to the conventional contents and web downloading and browsing services, usually conveyed according to a point-to-point broadcasting mode. For this, it makes use of the intrinsic point-to-multipoint broadcasting capacity of the satellite links, by adapting the mode of transmission of the multimedia contents according to a measured popularity, and by storing the most popular contents as close as possible to the satellite terminal.